1. Field
The disclosed embodiments relate to resonant oscillator circuits. More specifically, the disclosed embodiments relate to techniques for improving the efficiency of clipped pulse generation using resonant oscillator circuits.
2. Related Art
Oscillator circuits are commonly used to generate pulses in electrical systems. However, commonly used oscillator circuits can consume a significant amount of power, which is a disadvantage for systems in which reduced power consumption is desired, such as portable computing devices. To solve this problem, “resonant oscillator circuits,” which transfer energy back and forth between inductive and capacitive circuit elements, can be used to generate clock pulses without dissipating a significant amount of power. (For example, see U.S. Pat. No. 5,559,478, entitled “Highly Efficient, Complementary, Resonant Pulse Generation,” by inventor William C. Athas, filed 17 Jul. 1995.)
In the above-described resonant oscillator circuit, a stream of resonant pulses with a substantially sinusoidal shape is generated, and a switching device is used to clamp the output voltage of the resonant oscillator circuit to ground on the falling edge of each pulse when the pulse potential reaches zero volts. Input voltage across the resonant oscillator circuit's inductor and the switching on of the switching device may then reverse the inductor current from a negative value at the end of a pulse to a positive value determined by the duration of the switching device's on-time. In addition, the peak voltage of the resonant pulses may be determined by the amount of current in the resonant oscillator circuit's inductor at the time at which the switching device is turned off.
It is also highly desirable to hold the amplitude (i.e., peak voltage) of the pulses to a predefined constant level, in much the same way that the low signal level of the pulses is held constant. Design constraints on the peak voltage (e.g., from the load circuit driven by the pulses) may be one reason for clipping the output pulses. For example, the pulses may be used to drive a set of metal-oxide-semiconductor field-effect transistors (MOSFETs) with maximum operating voltage ratings. The pulses may thus be clipped to the MOSFETs' rated maximum operating voltage to mitigate degradation and/or reduced reliability in the MOSFETs.
To clip the pulses, a nonlinear element such as a Zener diode may be coupled to the output of the resonant oscillator circuit. In turn, the amplitude of the pulses may be clipped to the Zener voltage of the Zener diode. However, the Zener diode may dissipate power that normally oscillates between the load and the resonant oscillator circuit, thus increasing the power consumption and reducing the efficiency of the resonant oscillator circuit.
Hence, what is needed is a mechanism for increasing the efficiency of a resonant oscillator circuit that generates clipped pulses.